Pyupgrade to Python 3.9 (#4718)

* Pyupgrade to Python 3.9

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

graphs/minimum_spanning_tree_kruskal.py

@@ -40,7 +40,7 @@ if __name__ == "__main__":  # pragma: no cover
     edges = []
 
     for _ in range(num_edges):
-        node1, node2, cost = [int(x) for x in input().strip().split()]
+        node1, node2, cost = (int(x) for x in input().strip().split())
         edges.append((node1, node2, cost))
 
     kruskal(num_nodes, edges)